1. Field of the invention.
This invention relates to cans and in particular to a can of the kind comprising a body having an open top closed by a diaphragm.
2. Description of the Prior Art
Cans of the kind referred to above are sometimes used to contain products such as dried milk powder, instant coffee, ground coffee, and other products which will tolerate only relatively small increases in moisture content without losing their fresh condition and the diaphragms used with such cans are usually of paper, foil or plastics material, or combinations of such materials, secured to the cans by, for example, an adhesive which may be a heat-sealable adhesive preapplied to the diaphragms or to the cans. This kind of can has the disadvantage that the thin film of adhesive sometimes has insufficient bond strength and insufficient thickness to form an effective seal particularly in the region of the side seam of the can body. Further, during heatsealing adhesive tends to be squezzed out and to adhere to the lid which covers the diaphragm-closed end of the can and this sometimes results in the diaphragm being ruptured when the lid is removed.
It has also been proposed mechanically to secure the diaphragm, without the use of an adhesive, to a separate ring which is fitted in the end of a can and connected thereto by a double end seam, the can being closed by a lid of the kind known as a lever lid. Cans of this kind are more expensive because an additional component, the above mentioned ring, is required, and there is a disadvantage in that the diaphragm does not have a flat form, thereby creating risks of rupturing, particularly if creases are formed. Furthermore, this method reduces the sealing efficiency of the double end seam.
It is an object of the present invention to provide a can having an open top closed by a diaphragm and which overcomes the disadvantages of cans of the kinds just referred to.